The Observable<T> generic type must be provided with one type argument

I encountered the following 3 errors while working with the Angular 2 (TypeScript) code below. Can you provide suggestions on how to resolve them?

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { NgModule, Component } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpModule, Http } from '@angular/http';
import 'rxjs/add/operator/map';
import { Observable } from "rxjs/Observable";

@Component({
    selector: 'http-client',
    template: `<h1>All Products</h1>
  <ul>
    <li *ngFor="let product of products">
       {{product.title}}
    </li>
  </ul>
  `})
class AppComponent {

    products: Array<string> = [];

    theDataSource: Observable;

    constructor(private http: Http) {

        this.theDataSource = this.http.get('api/products/')
            .map(res => res.json());
    }

    ngOnInit() {
        // Get the data from the server
        this.theDataSource.subscribe(
            data => {
                if (Array.isArray(data)) {
                    this.products = data;
                } else {
                    this.products.push(data);
                }
            },
            err =>
                console.log("Can't get products. Error code: %s, URL: %s ", err.status, err.url),
            () => console.log('Product(s) are retrieved')
        );
    }
}

@NgModule({
    imports: [BrowserModule,
        HttpModule],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
})
class AppModule { }

platformBrowserDynamic().bootstrapModule(AppModule);

The errors are as follows:

  1. TS2314 Generic type 'Observable' requires 1 type argument(s).
  2. TS7006 Parameter 'data' implicitly has an 'any' type.
  3. TS7006 Parameter 'err' implicitly has an 'any' type.

Answer №1

myData: Observable<specificType>;

The variable specificType should ideally be a more precise data type that aligns with the values it is expected to produce.

Answer №2

By examining the source code of the Angular Http module, you will come across a method called request within the Http class.

Check it out here!

All the other methods such as get, post, etc. are built upon this request method. Furthermore, you'll notice that the request method returns an Observable with the generic type being Response class. This Response class is part of the Http module, so you can adjust your code like this:

import { HttpModule, Http, Response } from '@angular/http';
...
theDataSource: Observable<Response>;

If you prefer not to specify the type explicitly, you can simply use any as the generic parameter:

theDataSource: Observable<any>;

However, in my view, opting for strong typing is the better approach.

Answer №3

1) theDataSource: Observable; ->

theDataSource: Observable<any>;

2-3) To resolve the issue, you have two options:
- Add "noImplicitAny": false to your tsconfig.json
- Modify data => and err => to (data: any) => and (err: any) =>

Answer №4

In my opinion, the best approach in this situation is to define it as

theDataSource: Observable<Response>;
since that aligns with the type inferred from your work in the constructor. Using any should be avoided at all costs.

On a side note, although it may not be directly related to your current property, when working with methods you can utilize the following structure:

  type MethodPayload<T> = {
    something: string;
    data: T;
  }

  methodName<T>(payload: MethodPayload<T>) {
    // perform actions with payload
  }

Answer №5

Resolved the problem using this command: npm install @types/[email protected] --save-dev

Answer №6

Is it possible that the issue lies in the absence of angle brackets?

Observable(PhotosResult) rather than using Observable<PhotosResult>

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